For me, the thing with Expressive/Stoic is that it seems redundant (or at least strongly overlapping) with the Logical/Thinking vs. Emotional/Feeling dichotomy, which is already on the app under the same section. They might be slightly different, like Expressive vs. Stoic talks about your emotional range/intensity whereas Logical/Thinking vs. Expressive/Feeling talks about the way you evaluate things or make decisions -- in a logical way or based on how they make you feel. But it could be argued that Expressive and Emotional/Feeling = respond to things emotionally, Stoic and Logical/Thinking = respond to things in a way detached from emotion.

As I said earlier, my aim with the original Cheerful/Gloomy dichotomy was to get a feel of whether the person tends more toward smiles or more toward neutral faces/frowns, which is different than just how volatile their emotions are, I think?